Spence Stephanie L, Xu Zhengrui, Sainio Sami, Nordlund Dennis, Lin Feng
Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94035, United States.
Inorg Chem. 2020 Aug 3;59(15):10591-10603. doi: 10.1021/acs.inorgchem.0c01042. Epub 2020 Jul 23.
Single-crystal materials have played a unique role in the development of high-performance cathode materials for Li batteries due to their favorable chemomechanical stability. The molten salt synthesis method has become one of the most prominent techniques used to synthesize single-crystal layered and spinel materials. In this work, the molten salt synthesis method is used as a technique to tune both the morphology and Mn content of high-voltage LiNiMnO (LNMO) cathodes. The resulting materials are thoroughly characterized by a suite of analytical techniques, including synchrotron X-ray core-level spectroscopy, which are sensitive to the material properties on multiple length scales. The multidimensional characterization allows us to build a materials library according to the molten salt phase diagram as well as to establish the relationship among synthesis, material properties, and battery performance. The results of this work show that the Mn content is primarily dependent on the synthesis temperature and increases as the temperature is increased. The particle morphology is mostly dependent on the composition of the molten salt flux, which can be tailored to obtain well-defined octahedrons enclosed by (111) facets, plates with predominant (112̅) facets, irregularly shaped particles, or mixtures of these. The electrochemical measurements indicate that the Mn content has a larger contribution to the battery performance of LNMO than do morphological characteristics and that a significant amount of Mn could become detrimental to the battery performance. However, with similar Mn contents, morphology still plays a role in influencing the battery cycle life and rate performance. The insights of molten salt synthesis parameters on the formation of LNMO, with deconvolution of the roles of Mn and morphology, are crucial to continuing studies in the rational design of LNMO cathode materials for high-energy Li batteries.
单晶材料因其良好的化学机械稳定性，在锂电池高性能正极材料的发展中发挥了独特作用。熔盐合成法已成为合成单晶层状和尖晶石材料最突出的技术之一。在这项工作中，熔盐合成法被用作一种调节高压LiNiMnO（LNMO）正极材料的形貌和锰含量的技术。通过一系列分析技术对所得材料进行了全面表征，包括对多个长度尺度上的材料特性敏感的同步加速器X射线芯能级光谱。多维表征使我们能够根据熔盐相图构建材料库，并建立合成、材料性能和电池性能之间的关系。这项工作的结果表明，锰含量主要取决于合成温度，并随温度升高而增加。颗粒形貌主要取决于熔盐助熔剂的组成，可以通过调整其组成来获得由（111）面围成的规则八面体、以（112̅）面为主的片状、不规则形状的颗粒或这些形状的混合物。电化学测量表明，锰含量对LNMO电池性能的贡献比形貌特征更大，并且大量的锰可能对电池性能有害。然而，在锰含量相似的情况下，形貌仍然在影响电池循环寿命和倍率性能方面发挥作用。熔盐合成参数对LNMO形成的影响，以及对锰和形貌作用的解卷积，对于继续开展高能锂电池LNMO正极材料的合理设计研究至关重要。
